Numerous pressure sensors are currently known. More generally, it is possible to define a pressure sensor as being the element that will make it possible, by mechanical pressure, to deliver an electrical signal that can be used by a control circuit.
Pressure sensors have recently undergone increased development because of their expanded use as part of a touch screen. A touch screen indeed enables a user to accomplish different functions by exerting pressure on an interface panel with a finger or a stylus in a precise area indicated by a graphic and/or textual interface. In general, touch screens are thus suitable for recognizing a determined pressure in a determined area of the interface panel, and a control circuit connected to a software processing system of the electrical signal can thus interpret the determined pressure in relation to the graphic and/or textural interface area and thus activate desired operations.
It is possible to cite here the various commercial embodiments produced by the Apple company and which concern touch screens including a plurality of pressure sensors making it possible to detect the pressure exerted on a glass plate.
In their touch screen application, pressure sensors can be classified into two different categories.
Resistive-type pressure sensors include two plates each coated with layers or a plurality of pads made of an electrically conductive material and separated from one another by a layer of resistive material. When pressure is exerted on the plate with an exterior interface, the metal conductive pads or layers come into contact by means of the resistive layer, creating a modification in the electrical resistance, this electrical modification in a precise area being used to detect where the pressure has been exerted. In capacitive-type pressure sensors, electrical charges are accumulated on a glass plate with an exterior interface. When pressure is exerted on said plate, an excess capacitance is induced. This excess can be measured. The distribution of a plurality of pressure sensors over the entire surface of the plate makes it possible to determine the coordinates of the area on which the pressure has been exerted.
The inventors thinks that, for different applications, it would be beneficial to have a pressure sensor made using plastic technology, in particular because it enables flexible substrates to be envisaged. In addition, the inventor thinks that increasing the sensitivity of such pressure sensors could be beneficial.
The objective of the invention is therefore to propose a new type of pressure sensor capable of being made using plastic technology and of which the sensitivity can be increased.
Another objective of the invention is to propose a pressure sensor to be used as a basis for a touch screen.